Offshore wells commonly produce hydrocarbons of a wide range of compositions. Those molecules with at least five carbon atoms remain liquid at ambient temperatures and are transported by tankers to offloading facilities. Those molecules with four or less carbon atoms generally form gases at ambient temperatures.
In many cases the undersea well is too far from shore or an existing pipeline to make it economical to transport the gas through an auxiliary pipeline or to a consuming facility (e.g. power plant). Such gas is commonly referred to as marginal gas and has previously been flared (burned). More recent environmental concerns result in prohibitions against flaring of gas. It is possible to inject the gas back into the gas well, but this results in a progressively increasing percent of gas produced from the well, generally making reinjection uneconomical. It is possible to store all the gases in liquid form and at atmospheric pressure but this requires a very low temperature (about −160° C., or −260° F.) which is costly to reach and maintain. Storage at high pressure and moderate temperature to keep the gases liquid, is dangerous and costly. If the gases are transported in a gaseous state, then a very small mass of gas is transported.
There has been a suggestion to convert the gases to hydrates, wherein gas molecules are trapped in water crystals. The hydrates can be transported at moderately low temperatures (e.g. −10° C. to −40° C.) at atmospheric pressure, and they can form a slurry when mixed with crude oil or with water. One problem in converting gases into hydrates is that the economics are not favorable because there is no existing infrastructure for transporting and processing large volumes of hydrates. There are many facilities around the world for receiving LPG (liquid petroleum gas) which includes the heavier gases propane and butane, but few facilities for receiving lighter gases. Also, there are no large facilities for converting gas (and water) into hydrates, and there is presently experience with only small facilities. A system for storage and transport of marginal gas, in a safe and low cost manner based on existing gas handling infrastructure, would be of value.